Curious about global water innovations & regulation updates? Explore Water Channel →
Rispri LabsENGINEERING A CIRCULAR FUTURE

Free tool · Water and wastewater treatment design

Grit Chamber Design Calculator

A horizontal flow grit chamber keeps velocity near 0.3 m/s. Width = peak flow ÷ (velocity × depth), and length = depth × velocity ÷ settling velocity, plus 25 to 50% for turbulence. For 500 m³/h, 0.6 m depth and 0.2 mm grit, the channel is about 0.77 m wide and 13 m long.

Your inputs

Results update as you type. Example values are filled in.

m³/h

Provide one standby channel in addition.

m/s

0.25 to 0.4 m/s keeps organics moving while grit settles.

m/s

0.2 mm sand (SG 2.65): about 0.021 m/s. 0.15 mm: about 0.013 m/s.

m
%

How to use this calculator

  1. Enter the peak flow and the number of working channels.
  2. Keep horizontal velocity near 0.3 m/s.
  3. Set the settling velocity of the smallest grit you want to remove.
  4. Read the channel width, length and detention time.

How do you calculate the length of a grit chamber?

Cross section = Q ÷ vh; Width = cross section ÷ depth

L = d × vh ÷ vs × (1 + allowance)

A particle must fall the full depth in the time it takes water to travel the channel length. The allowance covers inlet and outlet turbulence.

Worked example

With peak flow 500 m³/h, working channels 1, horizontal velocity 0.3 m/s, grit settling velocity 0.021 m/s, water depth at peak flow 0.6 m, length allowance for turbulence 50 %:

Channel length: 12.9 m

The calculator also gives channel width 0.77 m; cross section area 0.463 m²; theoretical settling length 8.6 m.

Assumptions and limits

  • Ideal settling (Camp-Hazen). Real channels need the turbulence allowance.
  • For aerated or vortex grit chambers, use the manufacturer design curves.

Frequently asked questions

What is the velocity in a grit chamber?

About 0.3 m/s. Slower lets organic matter settle with the grit; faster carries grit through.

What is the detention time of a grit chamber?

Horizontal flow channels typically have 30 to 60 seconds at peak flow.

What size grit should be removed?

Most designs target 0.15 to 0.2 mm particles with a specific gravity of 2.65. CPHEEO uses 0.15 mm for Indian sewage.

References

  • CPHEEO, Manual on Sewerage and Sewage Treatment Systems (2013)
  • Metcalf and Eddy, Wastewater Engineering, 5th ed.

Built and maintained by the Rispri Labs engineering team. Last updated .